The London Underground has come to a standstill as a 24-hour strike causes travel chaos for rush hour commuters.

The biggest Underground walkout in Britain in over a decade led to people packing on to buses or walking to work, with business groups warning the strike will cost the capital's economy tens of millions of pounds.

The British government and London mayor Boris Johnson have criticised the strike action, but unions have pointed the finger at London Underground, and called for further talks to resolve the dispute.

Travellers there have described "absolute carnage" as they tried to get into work.

One commuter said police were called to a bus stop after the driver refused to move because his vehicle was too packed.

The traveller tweeted: "Absolute carnage on 113 bus. Driver refuses to drive as bus is too packed! Police was called and they just arrived! #tubestrike".

Others described delays on the roads, with many getting up hours earlier than normal and rerouting their journeys in an attempt to get in on time.

Some train platforms and buses were reported to be full before 6am.

Around 200 extra buses have been put on, while roadworks have also been suspended where possible. There are also extra river services, and Transport for London said trams will run a peak-time service all day.

There are also signalling problems at London Bridge, which is heaping further misery on passengers.

Thousands of striking workers from the four trade unions involved in the walkout have mounted picket lines outside stations this morning.

The strike is over the introduction of an all-night service on parts of the network from September.

It is scheduled to last until 6:30pm, but travellers have been advised it could take until Friday morning for services to return to normal.

The boss of London Underground, Mike Brown, said the walkout was "totally unnecessary".

He claimed LU had put together a "remarkably fair" pay offer for the introduction of the night service.

Steve Griffiths, LU chief operating officer, said: "We have put forward a very, very fair offer, which consists of an average salary increase of 2%, 1% or RPI (whichever is greater) for next year and the one after, plus a £500 night Tube launch bonus and an additional £2,000 bonus for night Tube train drivers."

Mr Johnson said most Londoners would look at the offer and "find it impossible to fathom why the unions are rejecting it".

LU has claimed it did not receive a response to the latest "fair and competitive" offer made on Monday, and urged the unions to put it to workers.

RMT general secretary Mick Cash said the strike had "rock solid" support from workers.

He said the disruption the strike "must force the Tube bosses back to the negotiating table to address the issues at the heart of this dispute".

"That means an end to the attempt to bulldoze through new working patterns that would wreck work/life balance and leave staff in safety critical jobs burnt out and stressed out at a time when Tube services are facing unprecedented demand," he added.

Wimbledon woes

London's economy could also be hit to the tune of hundreds of millions, according to some estimates.

The start of the strike affected tennis fans at Wimbledon, with people relying on public transport advised to leave before the end of Andy Murray's match.

A message on Centre Court's scoreboard said: "Due to industrial action, TfL advises that Underground services will be severely disrupted from the early evening onwards."

"Anyone relying on the Tube for onward connections should consider leaving as soon as possible."

Among those already affected by the disruption was actress Joan Collins who tweeted a picture and the post: "Stuck in traffic due to tube strike but the Tower of London still flies the flag."

Stuck in traffic due to tube strike but the Tower of London still flies the flag???????? pic.twitter.com/fk2X5KAEB2

— Joan Collins (@Joancollinsdbe) July 8, 2015

Others managed to find humour in the strike, with Felicity Morse tweeting: "Londoners have turned to savagery in the midst of the #tubestrike. Saw a man eat a two finger KitKat without breaking it in half lengthways."

However, some were not amused. Rohan Kallicharan wrote in a Twitter post: "Utterly NO sympathy for the Tube Drivers and Unions. Pure greed and political propaganda with no thought for anyone else #TubeStrike."

But others were more sympathetic. Scott Nelson tweeted: "This might make me unpopular but I back the #TubeStrike. Workers are standing up for their rights."